Carl Sagan (1934–1996) was an astronomer and science communicator. He organised the first physical messages to space (the Pioneer plaque and the Voyager Golden Record), presented the hugely popular TV series Cosmos (1980), and considered humanity’s long-term future in Pale Blue Dot (1994). He was also part of the team of researchers who first discovered the possibility of nuclear winter, and so became a leading voice of concern about the use of nuclear weapons.

Sagan’s words were often prescient and always poetic. In particular, I think he captures many ideas related to longtermism and existential risk as powerfully as anyone writing today.

I’ve tried collecting some quotations that stand out to me from Sagan’s work, though I’ve only read a minority of his published writing.

You can find a slightly more comprehensive version here. The website for Toby Ord’s book The Precipice contains a list of quotations pertaining to existential risk, which I partially borrowed from here. Michael Nielsen has also written some fantastic 'working notes' on Cosmos.

Cosmos: A Personal Voyage (1980)

Note that Cosmos was co-written with Ann Druyan.

Episode 1 — "The Shores of the Cosmic Ocean"

The cosmos is all that is, or ever was, or ever will be. Our contemplations of the Cosmos stir us — there is a tingling in the spine, a catch in the voice, a faint sensation, as if a distant memory, of falling from a great height. We know we are approaching the greatest of mysteries. The size and age of the cosmos are beyond ordinary human understanding. Lost somewhere between immensity and eternity is our tiny planetary home, the Earth. For the first time we have the power to determine the fate of our planet, and ourselves. This is a time of great danger, but our species is young and curious and brave. It shows much promise. In the last few millennia we have made the most astonishing and unexpected discoveries about the cosmos, and our place within it. I believe our future depends powerfully on how we understand this cosmos; in which we float, like a mote of dust, in the morning sky.

You can watch this opening scene here.

The surface of the Earth is the shore of the cosmic ocean. On this shore, we’ve learned most of what we know. Recently, we’ve waded a little way out; maybe ankle-deep: and the water seems inviting. Some part of our being knows this is where we came from; we long to return — and we can, because the Cosmos is also within us: we are made of star stuff.

We are the legacy of 15 billion years of cosmic evolution. We have a choice. We can enhance life and come to know the universe that made us, or we can squander our 15 billion year heritage in meaningless self-destruction. What happens in the first second of the next cosmic year depends on what we do — here and how — with our intelligence, and our knowledge of the cosmos.

Episode 13 — "Who Speaks for Earth?"

[Imagining human extinction] Maybe the reptiles will evolve intelligence once more. Perhaps, one day, there will be civilizations again on Earth. There will be life. There will be intelligence. But there will be no more humans. Not here, not on a billion worlds.

[T]he world impoverishes itself by spending a trillion dollars a year on preparations for war. And by employing perhaps half the scientists and high technologists on the planet in military endeavors. How would we explain all this to a dispassionate extraterrestrial observer? What account would we give of our stewardship of the planet Earth? We have heard the rationales offered by the superpowers. We know who speaks for the nations. But who speaks for the human species?

It's probably here… [Alexandria] that the word "cosmopolitan" realized its true meaning of a citizen, not just of a nation but of the cosmos. To be a citizen of the cosmos. Here were clearly the seeds of our modern world. But why didn't they take root and flourish?

Why, instead, did the West slumber through 1000 years of darkness until Columbus and Copernicus and their contemporaries rediscovered the work done here? I cannot give you a simple answer but I do know this: there is no record in the entire history of the library that any of the illustrious scholars and scientists who worked here ever seriously challenged a single political or economic or religious assumption of the society in which they lived.

The permanence of the stars was questioned. The justice of slavery was not.

It is our fate to live during one of the most perilous, and one of the most hopeful, chapters in human history. Our science and our technology have posed us a profound question: Will we learn to use these tools with wisdom and foresight before it's too late?

Will we see our species safely through this difficult passage so that our children and grandchildren will continue the great journey of discovery still deeper into the mysteries of the cosmos?

That same rocket and nuclear and computer technology that sends our ships past the farthest known planet can also be used to destroy our global civilization. Exactly the same technology can be used for good and for evil.

It is as if there were a god who said to us: "I set before you two ways. You can use your technology to destroy yourselves or to carry you to the planets and the stars. It's up to you."

‘Nuclear War and Climatic Catastrophe: Some Policy Implications’, 1983

Some have argued that the difference between the deaths of several hundred million people in a nuclear war (as has been thought until recently to be a reasonable upper limit) and the death of every person on Earth (as now seems possible) is only a matter of one order of magnitude. For me, the difference is considerably greater. Restricting our attention only to those who die as a consequence of the war conceals its full impact.

If we are required to calibrate extinction in numerical terms, I would be sure to include the number of people in future generations who would not be born. A nuclear war imperils all of our descendants, for as long as there will be humans. Even if the population remains static, with an average lifetime of the order of 100 years, over a typical time period for the biological evolution of a successful species (roughly ten million years), we are talking about some 500 trillion people yet to come. By this criterion, the stakes are one million times greater for extinction that for the more modest nuclear wars that kill “only” hundreds of millions of people.

There are many other possible measures of the potential loss—including culture and science, the evolutionary history of the planet, and the significance of the lives of all of our ancestors who contributed to the future of their descendants. Extinction is the undoing of the human enterprise.

Pale Blue Dot (1994)

Above: the pale blue dot in question, taken by the Voyager 1 spacecraft, 3.7 billion miles from the Earth. Sagan requested that NASA turn the spacecraft around to capture the image.​

Look again at that dot. That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every "superstar," every "supreme leader," every saint and sinner in the history of our species lived there-on a mote of dust suspended in a sunbeam.

The Earth is a very small stage in a vast cosmic arena. Think of the endless cruelties visited by the inhabitants of one corner of this pixel on the scarcely distinguishable inhabitants of some other corner, how frequent their misunderstandings, how eager they are to kill one another, how fervent their hatreds. Think of the rivers of blood spilled by all those generals and emperors so that, in glory and triumph, they could become the momentary masters of a fraction of a dot.

Our posturings, our imagined self-importance, the delusion that we have some privileged position in the Universe, are challenged by this point of pale light. Our planet is a lonely speck in the great enveloping cosmic dark. In our obscurity, in all this vastness, there is no hint that help will come from elsewhere to save us from ourselves.

The Earth is the only world known so far to harbor life. There is nowhere else, at least in the near future, to which our species could migrate. Visit, yes. Settle, not yet. Like it or not, for the moment the Earth is where we make our stand.

It has been said that astronomy is a humbling and character-building experience. There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly with one another, and to preserve and cherish the pale blue dot, the only home we've ever known.

You can watch a remastered recording of Sagan narrating the passage above here.

It might be a familiar progression, transpiring on many worlds—a planet, newly formed, placidly revolves around its star; life slowly forms; a kaleidoscopic procession of creatures evolves; intelligence emerges which, at least up to a point, confers enormous survival value; and then technology is invented. It dawns on them that there are such things as laws of Nature, that these laws can be revealed by experiment, and that knowledge of these laws can be made both to save and to take lives, both on unprecedented scales. Science, they recognize, grants immense powers. In a flash, they create world-altering contrivances. Some planetary civilizations see their way through, place limits on what may and what must not be done, and safely pass through the time of perils. Others, not so lucky or so prudent, perish.

Many of the dangers we face indeed arise from science and technology—but, more fundamentally, because we have become powerful without becoming commensurately wise. The world-altering powers that technology has delivered into our hands now require a degree of consideration and foresight that has never before been asked of us.

I do not imagine that it is precisely we, with our present customs and social conventions, who will be out there. If we continue to accumulate only power and not wisdom, we will surely destroy ourselves. Our very existence in that distant time requires that we will have changed our institutions and ourselves. How can I dare to guess about humans in the far future? It is, I think, only a matter of natural selection. If we become even slightly more violent, shortsighted, ignorant, and selfish than we are now, almost certainly we will have no future.

They will gaze up and strain to find the blue dot in their skies. They will love it no less for its obscurity and fragility. They will marvel at how vulnerable the repository of all our potential once was, how perilous our infancy, how humble our beginnings, how many rivers we had to cross before we found our way.

Billions and Billions (1997)

Billions and Billions (published 1997) was the last book Sagan wrote before his death in 1996.

Chapter 8 is titled “The Environment: Where Does Prudence Lie?”. It focuses on risks from climate tipping points and nuclear winter. But its ruminations on the consequences of extreme climate change go beyond that supposed cause.

[W]ith great powers come great responsibilities. Our technology has become so powerful that—not only consciously, but also inadvertently—we are becoming a danger to ourselves. Science and technology have saved billions of lives, improved the well-being of many more, bound up the planet in a slowly anastomosing unity—and at the same time changed the world so much that many people no longer feel at home in it. We've created a range of new evils: hard to see, hard to understand, problems that cannot readily be cured.

Sometimes even words like "fraud" or "hoax" are uttered about the dire scenarios. How good is the science here? How can the average person be informed on what the issues are? Can't we maintain a dispassionate but open neutrality and let the contending parties fight it out, or wait until the evidence is absolutely unambiguous? After all, extraordinary claims require extraordinary evidence. In short, why should those who, like myself, teach skepticism and caution about some extraordinary claims argue that other extraordinary claims must be taken seriously and considered urgent? Every generation thinks its problems are unique and potentially fatal. And yet every generation has survived to the next. Chicken Little, it is suggested, is alive and well. Whatever merit this argument may once have had—and certainly it provides a useful counterbalance to hysteria—its cogency is much diminished today.

Today we face an absolutely new circumstance, unprecedented in all of human history. When we started out, hundreds of thousands of years ago, say, with an average population density of a hundredth of a person per square kilometer or less, the triumphs of our technology were hand axes and fire; we were unable to make major changes in the global environment.The idea would never have occurred to us. We were too few and our powers too feeble. But as time went on, as technology improved, our numbers increased exponentially, and now here we are with an average of some ten people per square kilometer, our numbers concentrated in cities, and an awesome technological armory at hand—the powers of which we understand and control only incompletely.

Just how far along we are in working the various prophesied planetary catastrophes is still a matter of scholarly debate. But that we are able to do so is now beyond question. Maybe the products of science are simply too powerful, too dangerous for us. Maybe we're not grown-up enough to be given them. Would it be wise to give a handgun as a present to an infant in the crib? What about a toddler, or a preadolescent child, or a teenager? Or perhaps, as some have argued, automatic weapons should be given to no one in civilian life, because all of us have experienced at one time or another blinding if childish passions. If only the weapon were not around, it so often seems, the tragedy would not have happened. (Of course there are reasons people give for having handguns, and there may be circumstances in which those reasons are valid. Likewise for the dangerous products of science.) Now one further complication: Imagine that when you pull the trigger on a handgun, it takes decades before either the victim or the assailant recognizes that someone's been hit. Then it's even more difficult to grasp the dangers of having weapons around.

No species is guaranteed its tenure on this planet. And we've been here for only about a million years, we, the first species that has devised means for its self-destruction. We are rare and precious because we are alive, because we can think as well as we can. We are privileged to influence and perhaps control our future. I believe we have an obligation to fight for life on Earth—not just for ourselves, but for all those, humans and others, who came before us, and to whom we are beholden, and for all those who, if we are wise enough, will come after. There is no cause more urgent, no dedication more fitting than to protect the future of our species. Nearly all our problems are made by humans and can be solved by humans. No social convention, no political system, no economic hypothesis, no religious dogma is more important.

Except for millenarians of the various denominational persuasions and the tabloid press, the only group of people that seems routinely to worry about new claims of disasters—catastrophes unglimpsed in the entire written history of our species—are the scientists. They get to understanding how the world is, and it occurs to them that it might be very different.

You might think a different set of problems should have higher priority, or that there are a different set of solutions. But I hope you'll find in reading this section of the book that you're provoked into contemplating the future a little more. I don't wish unnecessarily to add to our burden of anxieties— almost all of us have a sufficient number— but there are some issues that not enough of us, it seems to me, are thinking through. This sort of contemplating the future consequences of present actions has a proud lineage among us primates, and is one of the secrets of what is still, by and large, the stunningly successful story of humans on Earth.

Concluding thoughts

I’ve strung a number of quotations together with a very similar message and tone. I’m worried that reading too many consecutively begins to feel saccharine or overly profound — empty calories. Of course, most of Sagan’s work (even ignoring his research output) was relatively more contentful and closer to the object-level. For instance: I love the section of Cosmos that explains Eratosthenes’ figuring of the Earth’s roundness. As a result, when these passages do appear, they stand out as contextualised and pointed departures. These are the parts in between: where we zoom all the way out, see things in some grand human story, ponder our failings and future.

Conjuring a sense of the profound isn’t as important as actually doing profoundly important things, but it is a useful starting point, which is why I’m interested in Sagan’s almost unique capacity for it. I’m not sure how many people Sagan influenced to become scientists, but more than 500 million people saw the original Cosmos series. It touched some kind of nerve.

Sagan answered the question he posed in the final episode if Cosmos: “who speaks for Planet Earth?”. To try doing this, and for a full tenth of the planet to listen, is an almost unique achievement.

Other than for inspiration and enjoyment, I’m not exactly sure about the upshot for effective altruism and longtermism. But:

1. I find it striking that I can list very few people who are even earnestly trying to create things that occupy a similar role to Sagan’s work^[1] today.
2. I think some themes that run through effective altruism and longtermism^[2]have the potential to be similarly compelling.

1. ^{^}

   Very wide in scope, scientifically literate, authentic, not unbearably pretentious.

2. ^{^}

   Messages to the effect that the appropriate reaction to major problems is to try solving them; that problems are solvable and have been solved; that dejection or mere guilt don’t achieve much unless they inspire action.